The present invention relates to an automatic brake booster which is used in a brake of an automobile or the like, and more particularly, to an improvement of a valve mechanism thereof.
An automatic brake booster comprising a valve body slidably disposed within a shell, a power piston mounted on the valve body, a constant and a variable pressure chamber defined across the power piston, a valve mechanism mounted on the valve body for controlling a switching of a flow path, an input shaft coupled to a brake pedal for movement therewith for causing a valve plunger, which forms part of the valve mechanism, to advance to switch the flow path, and drive means which also forms part of the valve mechanism and which causes a ring, that is engaged with the valve plunger as the latter is advanced, to advance to switch the flow path is known in the art (Japanese Laid-Open Patent Application No. 262,958/1992).
In an automatic brake booster of the kind described, the drive means generally comprises a solenoid.
With the automatic brake booster arranged in the manner mentioned above, the drive means may be operated to achieve a brake operation without the depression of the brake pedal. In a conventional booster, the valve mechanism and the drive means which switches a flow path thereof have been disposed as spaced from each other in order to avoid an increase in the size of the booster.
In view of the foregoing, it is an object of the invention to provide an automatic brake booster of a high reliability with an arrangement which is simple as compared with the valve mechanism of a conventional automatic brake booster.
Specifically, the present invention relates to an automatic brake booster comprising a valve body slidably disposed within a shell, a power piston mounted on the valve body, a constant and a variable pressure chamber defined across the power piston, a valve mechanism mounted on the valve body for controlling a switching of a flow path, an input shaft coupled to a brake pedal for movement therewith for causing a valve plunger, which forms part of the valve mechanism, to advance to switch the flow path, and drive means which also forms part of the valve mechanism and which causes a ring, that is engaged with the valve plunger as the latter is advanced, to advance to switch the flow path and further comprises a solenoid plunger disposed on the valve plunger to be displaceable with respect thereto and adapted to be integrally connected to the valve plunger at an advanced end position thereof, and a resilient member interposed between the solenoid plunger and the valve plunger for maintaining the solenoid plunger at the advanced end position.
With the described arrangement, since the solenoid plunger which is caused to advance by the drive means and the valve plunger, which forms part of the valve mechanism, are coupled by the resilient member to move together, operating the drive means allows the flow path in the valve mechanism to be switched to achieve an automatic brake operation without the depression of the brake pedal.
Consequently, a simplification of the arrangement of the valve mechanism in comparison to the prior art allows the reliability of the automatic brake booster to be improved.
Above and other objects, features and advantages of the invention will become apparent from the following description of several embodiments thereof with reference with the attached drawings.